The winding conductors of dynamoelectric machines are placed in slots in a laminated magnetic core. When currents flow in the conductors, magnetic fluxes occur across the slots which cause induced voltages and eddy currents in the conductor. Similar fluxes link the end turn portions of the conductor outside the slot, with some additional leakage flux from the rotor and stator, and cause similar induced voltages in the end portions. For this reason, the conductors of large machines are always of stranded construction, being built up of a substantial number of relatively thin strands to minimize the eddy current loss. The fluxes, however, are not uniform but vary radially in density so that the induced strand voltages vary from strand to strand and circulating currents due to these unbalanced voltages flow between the strands causing excessive losses and heating. For this reason, it is necessary to transpose the strands in order to cancel out as far as possible the unbalanced strand voltages to minimize the circulating currents and resultant heating.
Conducting bars or conductor bars in this technical field with transposed strands are commonly referred to as Roebel bars. These single conductor bars commonly contain a stack of two or four adjacent strands. Conductor bars have a rectangular cross-section with a smaller or narrower upper side and larger lateral faces. Conductor bars have a length of several metres depending on the electric machine to be applied. The mechanical impact of the transposition of the strands is that the surface structure of the small or narrow side of the conductor bar becomes uneven. This uneven surface of the conductor bar in this fabrication step complicates the wrapping of the main insulation layer and ends up in undefined electrical field strengths. To the end of obtaining a homogeneous surface a putty is applied to the surface of the conductor bar before wrapping the main insulation around the conductor bar. As a tool, to apply the putty, rectangular rods from steel are aligned along the conductor bar with putty. A disadvantage of this fabrication method is that the conductor bar is sharp-edged in the area at which the putty is applied. This makes necessary a further fabrication step of polishing the edges. The polishing step is commonly done manually and does not always result in an even and sufficient quality for an increased high electrical field strength design. Undefined radii and edges enhance the electric field strength undesirably leading to a reduced life time of the respective conductor bar.